Safety bus duct plug



Aug. 7, 1962 J. B. cA'rALDo ETAI.l 3,048,672

SAFETY Bus DUCT PLUG Filed Nov. 9, 1959 14 sheets-sheet 1 Aug. 7, 1962 J. B. cATALDo ETAL 3,048,672

SAFETY Bus DUCT PLUG Filed Nov. 9, 1959 14 sheets-sheet 2 Aug; 7, 1962 J. B. cATALDo ETAI. 3,048,672

SAFETY Bus DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 3 Aug. 7, 1962 J. B. cATALDo ETAL 3,048,672

SAFETY BUS DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 4 /dm M .4f/www J. B. cATALDo ETAL 3,048,672

Aug. 7, 1962 SAFETY BUS DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 5 EIT-EEA- Aug. 7, 1962 J. B. CATALDO Em. 3,048,672

SAFETY BUS DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 6 m11- EE-.1.5.

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SAFETY BUS DUCT PLUG Aug. 7, 1962 Filed Nov. sa,k 1959 J.B.CATALDO ETAL SAFETY BUS DUCT PLUG 14 Sheets-Shaml 10 Ilm Aug. 7, 1962 J. B. CATALDO ETAL SAFETY BUS DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 11 MM, M

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J. B. CATALDO ETAL SAFETY BUS DUCT PLUG Filed NOV. 9, 1959 14 Sheets-Sheet 12 Allg- 7, 1962 .1. B. cATALDo ETAI. 3,048,672

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SAFETY Bus DUCT PLUG Filed Nov. 9, 1959 14 Sheets-Sheet 14 MM @f4 l vJ/a V1 --m il y 1 CU {o} mi; J/ l I I l INVENTORS maw 9. Wr/a0@ @MM/M W fig a M95 1United States Patent Oilice 3,048,672 Patented Aug. 7, 1962 3,048,672 SAFETY BUS DUCT PLUG John B. Cataldo, Birmingham, Robert W. Thomas, St. Clair Shores, Michael L. Mead, Detroit, and Norman Shaclnnan, Oak Park, Mich., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Nov. 9, 1959, Ser. No. 851,776 le Claims. (Cl. o-Sil) The instant invention relates to bus duct electric distribution systems in general and more particularly to a novel construction whereby the hazards of plug installation and removal are substantially eliminated.

Bus duct as an electric distribution system includes as one of its prime functions, an ability to provide areas along its length whereby devices can be inserted or plugged in for tapping off power to specific loads. These areas constitute cut-away portions of the duct enclosure over which a door is placed to close the area when a plug is not in position. While there has been no historic question regarding the effectiveness of a plug-in bus duct system for supplying power to individual loads, there have been many instances which attest to the lack of safety inherent in the installation procedures required for many types of plugs. Accidental contact by a metalllic object or tool between energized bus bars, or between a bus bar and the duct enclosure has resulted in electrical flashovers which have damaged equipment and created injuries to personnel. The probability for such accidents can be shown to be relatively high when the required installation sequence is examined closely.

The usual action that is iirst taken in installing a plug device of the prior art is to open the door over the plugin area. Many doors require the engagement of a hand tool for this purpose. Slippage of such a tool into the plug-in area has caused many electrical shocks and power arcs when the tool accidentally contacted a bus bar. Greatly increasing the probability of such an occurrence is the fact that the installer is holding a relatively heavy plug in one hand while attempting to open the plug-in access door with the other hand, meanwhile balancing itself on a tall ladder.

After the door has been opened, the plug must be aligned properly with the plug-in opening and then pushed into position so that the linger contacts engage the bus bars. The installer must balance or hold the plug against the duct with one hand, while trying to insert fastening screws, or to otherwise place a fastening means into position with the other hand. During these actions, there have been instances of damage to finger contacts from improper alignment, dropping of the plugs because of insufcient temporary support, dropping of fastening elements, such as screws, when attempting to install them with one hand, and a variety of other nuisance troubles which greatly increase installation time and contribute to the improper functioning of plugs.

In addition to these mechanical problems, there have been instances of electrical failures from shocks and power arcs when attempting to insert the plugs with internal switching contacts in the On position and a load connected. This occurrence is quite prevalent when plugs are pre-wired, or when plugs are changed from one location to another. In such instances, an arc is formed as the linger contacts engage the bus bars. Such arcing can cause a power arc to start by the accumulation of ionized gases Within the contines of the plug-in area.

A third problem associated with the use of plugs in prior art plug-in bus duct has to do with removal of plugs from the duct. The mechanical actions regarding removal of lfastening means, lack of support, etc. are

similar to those described previously, although in reverse, and create similar hazards. In addition, there is the electrical hazard of starting a power arc if the plug is removed while the switching contacts are in the On position and a load is still connected. The load is broken by disengaging the linger contacts from the bus bars. The ionized gases that result can cause power arcs as previously described. Hazards to personnel from such arcs are greater during removal of the plug than when inserting the plug. In the latter case, inserting the plug results in a partial block of the plug-in opening so that any electrical flash is screened somewhat from the face, hands, and body of the installer. This is not true when a plug is removed under a connected load condition and the plug-in area may be completely open.

Once a plug has been removed, the door is not infrequently left open for reasons of lack of time, jamming of the door, and Ia variety of other causes. The same possibility of tool insertion exists as previously mentioned. In this case, however, it is not only Ifor the installer that this hazard exists, but 4for any other personnel or cause not associated with actively inserting a plug such as traveling canes, equipment, material, etc. Finally, the hazard of leaving plug-in doors to open also extends to the undesirable entrance and accumulation of dust and other foreign matter within the bus duct.

The prior art has attempted to solve the above noted problems by providing plug devices in which the contact fingers are part of an assembly Within the plug case which can be made to extend or retract the fingers into and out of engagement with the duct bus bars. This assembly required a complicated operating mechanism which too often failed in view of the -fact that it was infrequently used.

In contrast the instant invention solves the above noted problem by utilizing a simplified construction enabling the plug unit to have contact fingers which are stationary with respect to the plug case. This is accomplished by providing the duct and plug of the instant invention with the following features either alone or in combination:

(l) Temporary support means,

(2) Plug-in opening alignment,

(3) Final fastening means,

(4) Interlock for duct doors and p (5) Load break switch interlock means.

The temporary support means comprises a hook whereby a plug unit can be self-supported in an intermediate postion by the enclosure of a bus duct section from which, after other yfunctions are accomplished, the unit may be moved into or out of its nal inserted position. Such temporary support permits support of the plug-in unit on the duct at a position other than its linal position; permits alignment of plug contact lingers and other associated parts for iinal positioning without any manual support of the unit; makes it possible to wire the plug-in safely in its intermediate position before the contact fingers engage the bus duct conductors; reduces the probability of accidental contact with the conductors of the bus duct by a tool or other metallic object by partially covering the plug-in area with the body of the plug-in device when Ithe plug-in access door is moved; creates a safer means for engaging and disengaging the plug contact lingers with the bus bars by allowing freedom in the use of both hands of the installer for this function; and permits the plug-in yaccess door to be safely opened or closed with the plug in a self-supporting intermediate position.

The plug in opening alignment means comprises forma- -tions in the bus enclosure which cooperate with temporary support means hook to position the plug so that upon final positioning of the plug its contact lingers will always extend through the access opening in the duct housing without striking the duct housing.

The final fastening means comprise screw means which engages cooperating thread openings of the duct housing and may also include screw means which bears against the duct housing at strategic points whereby the contact fingers are maintained in engagement with the bus bars and the plug is iirmly secured to the duct.

The interlock for the duct doors comprises means by which a cooperative member or members are provided between a plug-in unit and a plug-in access door on the bus duct so that the door may be opened or closed only when the plug-in unit is in an intermediate position. For unusual instances of inspection, emergency, or use of nonstandard plug devices, -both the interlock member and/or door can be moved to another position to obtain voidable action. Thus, the plug-in access doors are kept closed when a plug-in unit is not in an inserted position; hence, exposure of bus bars for accidental short circuit contact with a metallic object, and entrance of dust, dirt, etc., is eliminated; exposure of bus bars for accidental short circuit contract with a metallic object during installation of plug is virtually eliminated since the plug unit blocks the opening during the sequence or" engagement of interlock with the door and door opening; there is assurance that a plug access door is closed during the initial phase of plug installation since engagement of the interlock member can only be made with the door closed; accidental short circuit contact between the door and plug unit fingers when lthe plug is in its `full engaged position is eliminated (that is, the door can be closed) by an interference between the door and interlock member; a safer plug retraction sequence is obtained since a stop is provided between the interlock member and the door when the plug is being retracted. This stop provides a temporary and partial support of the plug device; and complete safety from bus bar exposure when la plug is removed 'from the duct is obtained since the plug-in access door must be closed before the plug can be completely removed from the duct.

Load break switch interlock is achieved by an interaction of `a member from the plug with the duct enclosure whereby the contact fingers of the plug 'are prevented from engaging `or disengaging the duct bus bars if the plug switching contacts are in the closed position. Such an interaction can be made voidable. During insertion of a plug into bus duct, accidental energization of a plug load by contact between 4fingers and the duct bus bars is eliminated; during the act of removing a plug from bus duct, accidental breaking of a plug load between fingers and the `duct bus bars is eliminated; and safety of personnel and elimination of damage to equipment from power arcs started between finger contacts and bus bars is obtained.

Accordingly, a primary object of the instant invention is to provide a novel construction for a bus duct plug unit including temporary support means whereby the plug is supported in an intermediate mounting position and thereafter pivoted into final mounting position.

Another `object of this invention is to provide novel means including the temporary support means for bringing the plug unit contact fingers in alignment with an access opening of the duct.

Still another object of this invention is to provide novel means for maintaining a plug unit in its final mounting position with respect to the duct.

A further object is to provide novel means for interlocking the `duct access doors responsive to the position of the plug unit relative to the duct.

A still lfurther object is to provide novel means for interlocking the load break switch responsive to the position of the plug unit relative to the duct.

These as Well as other objects of the instant invention shall readily become apparent after reading the following description of the accompanying drawings in which:

FIGURE 1A is a plan view of a plug mounted to a duct in an intermediate position.

FIGURE lB is a load end view `of the duct and plug of FIGURE lA with the plug in final fastening position.

FIGURE 2A is a plan view of a modification `of the plug illustrated in FIGURE lA.

FIGURES ZB and 2C are end views of the duct and plug of FIGURE 2A looking at the line and load ends, respectively.

FIGURE 2D is a plan View of the plug and duct of FIGURE 2A with the plug in final position.

FIGURE 12E is a line end view of the plug of FIG- URE 2D.

FIGURE 3A is a plan view of a plug mounted to a duct in a temporary position with the plug utilizing side hooks as a temporary fastening means.

FIGURE 3B is a load end view of the plug and duct of FIGURE 3A.

FIGURES 3C and 3D are cross-sections illustrating in detail the hook arrangement of FIGURE 3A.

FIGURE 3E is a perspective view of a plug mounted -in a temporary position to a duct with the duct including slots for locating a plug.

FIGURE 3F is a perspective similar to FIGURE 3E wherein the duct includes embossments for locating the plug.

FIGURE 4A is a plan view or" a plug mounted to a duct in an intermediate position with the plug including a two piece construction for effecting temporary fastening.

FIGURES 4B and 4C are end views of FIGURE 4A looking at the line and load ends, respectively, of the plug.

FIGURE 4D is a plan view of the plug and duct of FIGURE 4A with the plug in final position.

FIGURES 4E and 4F are plan views of a modified construction of the plug illustrated in FIGURE 4A. In FIG- URE 4E the plug is mounted to the duct in the intermediate position and in FIGURE 4F the plug is in final position.

FIGURES SA-SC are plan and end views of a load and a line end, respectively, of a plug and duct construction which is a modification of the construction illustrated in FIGURE 4A.

FIGURE 6 is a load end view of a plug mounted to a duct with the plug including two hooks for temporary fastening.

FIGURE 7 is a plan view illustrating an embodiment wherein a simple bracket is utilized to limit the extent to which the plug may pivot away from the duct.

FIGURE 8A is a plan view and FIGURES 8B-8D are load end views illustrating various embodiments for final fastening of the plug to the duct. All of these embodiments utilize a simple screw means.

FIGURE 9 is a modification of the embodiments illustrated in FIGURES 8A8D.

FIGURE l0 is a line `end view illustrating a modification of the embodiment of FIGURE 9.

FIGURES 1l and l2 are plan views of a plug mounted to a duct. These figures illustrate an embodiment for final fastening on the load end of the plug whereby slack between plug and duct is eliminated.

FIGURES 13A-13E illustrate various embodiments for final fastening at the line end of the plug. FIGURES 13A, 13C and 13E are plan views of a plug mounted to the duct of FIGURES 13B and 13D which are side views of the duct.

FIGURES 14A-14E illustrate a door interlock arrangement. FIGURE 14A is a plan view of the plug mounted in intermediate position to the duct, FIGURES 14D and 14E are line end views, while FIGURES 14B and 14C are elevational views of the duct. In FIGURE tl4B the access door is closed and in FIGURE 14C the access door is opened.

FIGURES l5A-l5C illustrate another embodiment of a `door interlock means. FIGURE A is a line end View while FIGURES 15B and 15C are elevational views. In FIGURE 15B the access door is closed while in FIG- URE l5C the access door is opened.

FIGURES 16A-16D illustrate another embodiment of a door interlock means.

FIGURES 16E-16G illustrate the relative positions between the plug door interlock linger and the Z-shaped slot of the `door for various positions of the door.

FIGURES 17A-17C are similar to FIGURES 16C-1 6G and illustrate a modified door interlock construction.

FIGURES 18A-18C illustrate an interlock arrangement between a load break switch and the door of the duct. FIGURES 18A -and 18B are plan views of the plug -mounted to the duct while FIGURE 18C is an end view of the plug. In FIGURE 18A the load break switch is in the Off position while in FIGURE 18C the load break switch is in the On position.

FIGURES 19A-19C illustrate a modified construction for a switch interlock. FIGURE 19A is a plan view of a plug mounted in intermediate position to a duct while FIGURES 19B and 19C are elevational Views of the duct of FIGURE 19A.

FIGURE 2O is a line end View of a plug illustrating a modied switch interlock arrangement.

FIGURES 21A and 21B illustrate a modification of the switch interlock arrangement of FIGURE 20. In FIGURE 21A the plug is in the intermediate position while in FIGURE 21B the plug is in final position.

FIGURE 22 is a fragmentary side elevation of a duct including the door over the access opening.

FIGURE 23 is a cross-section taken through line 23- 233l of FIGURE 22 looking in the direction of arrows 213-23 FIGURE 24 is a rear view of a plug especially constructed to be mounted to the duct of FIGURE 22.

FIGURE 25 is a load end View of the plug of FIGURE 24.

FIGURE 2.6 is a bottom view of the plug of FIG- URE 24.

FIGURE 27 is a fragmentary perspective view illustrating the front of the plug of FIGURE 24 at the line end thereof.

FIGURE 28 is a plan view of the duct access door.

FIGURE 28A is a view showing the top edge of the door of FIGURE 28.

FIGURE 29 is a side View of the duct with the access door removed to show the shape of the access opening.

FIGURE 301 is a perspective View of the positioning door interlock key forming part of the plug of FIG- URE 24.

It is to be understood that in the schematics of FIG- URES lA-ZlB portions of the duct and plug have been omitted when not essential to the particular feature under consideration. FIGURES 22-30` are detailed drawings illustrating a duct and plug incorporating the broad features of the instant invention.

It is also to be understood that reference to the front of the plug means the surface of the plug facing the duct; reference to the line side of the plug means the side of the plug case nearest the contact fingers, and reference to the load side of the plug means the side of the plug case furthest from the contact fingers since this is usually though not necessarily, the side of the case through which the load conductors extend.

Temporary Support Means yin opening of the duct 102 while the term self-supported has reference to the fact that the plug is not supported by the installer or any special tool. A fixed hooking CTI member 103 extends from the load end of the case 101 to engage a rail 104 on the top portion of duct 102. Flanges 105 extend from the top and bottom of the case 101 to rest against the fiat portions 106 of the top and bottom of the duct 102. The hook 103 serves to support the plug vertically, while iianges '105 hold it horizontally in line with the duct 102. The plug 100 can be swung into position against the duct 102 so that fingers 107 enter plug-in openings 108. During this action, the plug 100 pivots about line 109.

A second method, shown in FIGURES 2A-2E, employs one top load end fixed hook 111 and one extended top line end fixed hook 113. Here fixed hook 111 is again located on the load end of plug 112. The longer hook 1113 is attached to the line end of the plug 112. Both hooks 111, 113 are used to support the plug in its intermediate position. Vertical stability is obtained by resting edge 114 against the side of the duct 102. The plug 1.12 is swung into position by pivoting about edge 114. When this occurs, hook 113 rides over the top of the duct 102 as shown at 116. In this method, no flanges are required as in the previous method since the line hook 113 provides the necessary vertical stability.

A third method of self-support employs wings or side hooks (FIGURES 3A-3D) which enter slots .118 in the side of the duct enclosure 102. These slots 118 are just long enough to accommodate the base of the wing 117 as shown in the enlarged view, so as to limit longitudinal movement of the plug 100:1 when in final position on the duct 102. The tip of the wing -11'9 is elongated so that a hook locking action is obtained. A top flange 120 is also provided to obtain longitudinal stability and positioning for the plug 100m A fourth method, yFIGURES 3E, 3F employ slots 121a or embossments 122a in the duct enclosure for cooperation with a top load end hook 123. As shown in FIG- URE 3E, the duct enclosure 121 contains a series of slots 12101 into which a fixed top load end hook 123 can be engaged. A top flange 1-24 assists in horizontal stability of the plug 100. Alternatively, embossments 12241 can be placed lalong the inside vertical portions of the duct enclosure 122 as in FIGURE 3F.

A fifth method, FIGURES 1A-4D illustrates a two piece plug housing. A plug case 121 containing contact fingers, switch mechanism, etc. is pivoted at its load end at 122 to a second body or enclosure 123. 'Ihis enclosure consists of a top flange 124,r a bottom ange 12S, and a tie member 126 at the line end forming an open ended box into Iwhich plug body 1211 can lit. The top flange 124 is formed to provide a continuous hooking edge 127 along its length 128 for temporary support of the plug device on the duct 102. Alternatively individual hooks, as at 103 in FIGURE lA, can be employed at both the line and load ends of the top flange 124. Stability of the plug in its temporary or intermediate position is provided by resting edge 129 of the -plug body '121 against the side of the duct 102, by the edge '126e of tie member 126 against the side of the duct 102, by the top iiange hook 127 over the top of the duct 102 and .by resting the line end of the plug body 121 on the bottom flange 125.

In order to coordinate the relative movement of the twe elements of a two piece plug to obtain better guiding, and to limit the outward position of the plug body, slots 130 are placed in the .top and/or bottom flanges 124 and 125. Pins 131, permanently fixed to the plug body body 121, ride in these slots and provide guiding and stop positions.

To assist in installing the plug y121 in its temporary position, it is desirable to lock the plug body 121 to the enclosure, especially in the open position. This is done by biasing guiding pin into locking grooves at the ends of the slot in the flange. One means of accomplishing this is shown in FIGURES tE-4F. Pin 132 is biased into groove extensions 133, representing the limits of the acfiaera 7 open and closed positions of the plug body 121. Unlocking consists of manually pushing the pin 132 into the main portion of the slot 130 and moving the plug 121 away from duct 102.

A sixth method for obtaining temporary positioning of a plug device is shown in FIGURES SAwSC. A two piece unit is again used, except that the flange enclosure is replaced by a plate 134 slidably attached to the line end of plug lbody 135. This plate 131i contains a hook member 136 which, together with a stationary hook 137 at the load end of the plug body 135 provides the temporary support. Slots 138 in the end plate 134, and stationary pins "139 in the plug body 135 provide the guiding and limit stops for the relative motion and supporting between the end plate 134 and plug body 135. Spring biased pins and end grooves in the slots can be employed for locking purposes in the closed or open plug positions as described and shown in FIGURES 11E-4F.

In each of the six methods for temporary support previously described, it is to be noted that a common element exists that provides both a stability of support for the temporary positioning,y of the plug on the duct, and a point about which the plug is pivoted for rotation into its final or inserted position. This common element is the positioning of the load edge of the plug against the side of the duct, as at 1119 in FIGURE lA, 114- in FIGURE 2A, 118 in FIGURE 3A, etc. It is also to be noted that each of the siX methods incorporate hooking means that engage the top of duct 2, the shape of which is merely an offset or ledge against which the hook can rest. These are the simplest arrangements for the more common duct installation condition Where bus duct will be horizontally supported with plugs to be inserted into the sides of the duct.

There are two other duct installation conditions that are sometimes employed which may require additional elements on the plug device to achieve a self-supporting condition -in its temporary position. The trst is a horizontal run where plugs will be required to be installed to the underside of the duct. This is typified by the duct being placed against a ceiling with the plug-in areas facing downward. For this condition, a releasable hook 140m can be added to the load end of the plug 140 opposite a fixed hook 141 as shown in FIGURE 6. Such a hook is all that would be necessary for the temporary support methods of FIGURES 2A, 4A, and 5A where a stationary hook is also provided on the line side of the plug. A three point support is thus obtained. It is obvious that another releasable hook can be placed on the line side of the plug. Such an addition would provide better stability.

For the temporary support method of FIGURE lA where a single load hook and flange combination is used, a bottom load end releasable hook and a plate extension from the load end of the plug could be employed. This is shown in FIGURE 7. Extension 142 bears against the side of the duct 102 when the plug 142a hangs down. This same type of extension can be used in the construction of FIGURE 3A.

The second type of duct installation condition that requires additional consideration for temporary self-support of the plugs has to do with riser applications where the duct is mounted vertically. With the support method of FIGURE 3A, vertical positioning of the plug is readily obtained by engagement of wings 117 into slots 118 in the side of the duct enclosure 102. A support extension from the load end of the plug, as by 142 in FIGURE 7, can be added to prevent the plug from swinging too far from the duct 102. Vertical support of other plug designs incorporating stationary and releasable hooking means, such as shown in FIGURES 1A, 2A, 4A and 5A, can be accomplished by providing slots or embossrnents in the duct case for engagement -by the hooks of the plug. Two such slot areas were shown in FIGURES 31E-3F. Slots can be employed for ventilated bus duct, while embossments would be required for totally enclosed duct. The top line side hooks of FIGURES 2A, 4A and 5A assist in preventing the plug from swinging away from the duct. The design of FIGURE lA will require a support extension from the load end of the plug, as at 1412` in FIGURE 7 for the same reason as was necessary for the construction of FIGURE 3A.

Final F astenng M cans Having developed methods by which plugs can be placed in a temporary, intermediate, or open position, it was desirable to employ some of the elements of those methods to assist in securing the plug to the duct in its final or closed position by means that are rapid and positive. These means can be divided into those necessary to attach the load end of the plug and those necessary for the line end. `Considering rst the load end, it has been found that the simplest approach is to rely on the top `fixed load end hook `described previously, with no additional attachment screws. Since this hook has the correct dimension to envelop the support ledge or offset on the duct or the slots or embossments of the duct enclosure, the load end of the plug will reset fairly snug against the duct when the line end has swung into its nal position.

With heavier plugs of higher capacities a more positive holding means is added at the bottomy load end of the plug. This can be accomplished by including a releasaible hook at the bottom load end as previously described in FIGURE 6. Alternatively a locking pressure screw 1'41a (FIGURE 8) can be employed threaded -into a plug case flange member 141b. When the screw 141e is tightened, it can bear against the duct enclosure surface as shown in FIGURE SB. Also it is possible to emboss and tap a por-tion of the ange 41C (FIGURE 8D) sothat a screw Mld can bear against the corner 141e of the odset. Tightening of the screw will draw the plug against the duct. Further, it is also possible to provide a depression 1411 (FIGURE 8B) on the duct against which a screw 141g on the ilange of the plug can bear in pressure and locking relationship. The pressure screw arrangements described can be located at or near the load end of the plug.

Other methods for locking the load end of the plug incorporate different types of hooks. In the embodi- V ment of FIGURE 9, a releasable hook 148 is made retractable and operable by a screw 149 in a bracket 150 on the load end plate of the plug. This screw enters a threaded end 151 of the hook and when tightened will draw the plug tight against the `duct 102. Alternatively, the end plate 152 (FIGURE l0) is shaped with an eX- tension 153 to bear against the duct enclosure 102 so that tightening screw 149 will transfer some of the clamping force to the stationary hook 154.

Still another means of obtaining clamping pressures on the load side of the plug is to place a spring member 15S (FIGURE ll) along the front of the plug 15511 near the load side and to employ a bottom load end releasable hook as in `FIGURE 6. When the plug 155a is moved to its iinal position, force will be provided by spring 155 to take up any looseness in the load hook members.

A further means of accomplishing the load end clamping function is to employ an extension 156 (FIGURE l2) from the end plate of the load e-nd of the plug 156a that accommodates a screw 157 which can be turned against the side of the duct enclosure 102 so as to draw the hooks up tight. Extension 156 can be the same piece 142 as shown in FIGURE 7 `for the temporary positioning o-f the plug in vertically installed duct. A top load fixed hook and a bottom -load releasable hook are necessary in this construction.

Considering next the means for final support or fastening of the line end of the plug, as illustrated in FIG- URE 13A, a flange 143 is placed on the line end of the plug 143a and accommodates at least one fastening screw .9 144 which can enter a mating threaded hole in the side of the duct 102. This same screw 144 can enter a hole or slot in the plug-in access door 145 to keep the door from closing when plug 143a is in position. Thus, no other locking or detent means is necessary for the open position of the door 145,

The two piece plug designs of FIGURES 4A and 5A can also employ a flange as part of the plug body so that the plug body itself is directly fastened to the duct. FIGURES 13C-13D illustrate one arrangement. The tie member 126 of FIGURE 4A is extended away from the line end as shown at 14561 of FIGURE 13C. This makes room available for a liange 14511, -attached to plug body 145e, to swing into position against the side of the duct 102. for fastening purposes. Similarly, the end plate 134 o-f FIGURE 5A can be made to be retractable inside the plug lbody 145e as shown in FIGURE 13E. The end plate 145d, retractable Iwithin the plug, body 145e, makes it possible for a flange 145i to be attached to the outer line end of the plug for fastening purposes as previously described.

Another method for line end attachment is to use the pressure locking screw means of FIGURE 8D at or near the line side of the plug on a top flange or on a topy 4and bottom flange.

A third method for` line end attachment is to employ a releasable and retractable bottom line end hook as previously described with respect to FIGURE 9. This is adaptable directly to the plug -designs of FIGURES 4A and 5A where a top -lixed line hook is employed. Alternatively, the pressure point method of FIGURE 10 can be added so that increased clamping of the top fixed hook can be obtained.

A fth method would include a releasable top line hook, particularly to the plug design of FIGURES 1A and 3A which, with a bottom releasable and retractable line hook, would per-form an adequate line end clamping function. The pressure point method of FIGURE 10 can be added `for increased clamping of the top line hook.

A sixth method would utilize the plate extension of FIGURE l2 attached to the line end for a pressure locking screw against the side of the duct. This screw can also engage a hole in the door so that the door may be prevented from -being closed while the plug is attache-d to the duct. This method is applicable with top and bottom releasable line end hooks to plug designs of FIGURES 1 land 3, and to the two piece plug designs of FIGURES 4 `and 5 having bottom releasable line end hooks.

Alignment With Plug-in Opening Properly aligning the contact fingers of a plug to the plug-in opening is an important safety consideration since it is desirable to eliminate any possibility that the contact lingers will contact the bus bars and the edges of the plugin opening at the same time. In the plug design of FIG- URE 3A such alignment is automatically obtained by the prelocation of the slots in the duct enclosure to accept the side wings. For all other plug designs, FIGURES 1A 2A, 4A and 5A where hooks are employed on the load side of the plug, cooperating and prelocated slots serve for alignment purposes, such as those illustrated in FIG- URES 31E-3F. It is to be noted that the cooperation of load end hooks and slots in the above general scheme occurs before the plug is pushed into its final position; hence, alignment is secured before the Contact lingers enter the plug-in opening.

It is also possible to place an alignment linger 158, FIGURES 14A-14D, `on the line end of plug 158a to cooperate with a notch 159 in the plug-in opening 157a of duct enclosure 159a. By coordinating the door 160 and plug-in opening notch 159, lthe contact linger 158 cannot extend into the opening 157a until the door 160 has been moved out of the way toward the left of the opening. Finger 158 also can be made to serve another function in that the door 160 canot be closed with plug 158a in its closed or inserted position. This prevents any possible short circuit between contact lingers 160 and the door edge While the contact fingers engage the bus bars. A further additional function of an alignment linger is that of engaging a door release spring (not shown).

A modification in the placement of an alignment finger is obtained by making the linger as part of the tie plate or end plate of the two-piece plug designs of FIGURES 4A and 5A. FIGURE `14E shows such a construction adapted to the end plate type of plug of FIGURE 5A. An extension 160a is made part of the end plate 160b and lacts as a linger to enter a slot in the duct enclosure. The advantage of this method is that no further entrance of the linger into the duct occurs as the plug 160C is pushed into an inserted position. This is to be contrasted with the previously described construction where the locating linger is made part of plug body 160C and must enter the duct enclosure when the plug is pushed against the duct. To avoid this latter condition, however, it is possible to construct the linger so as to be spring biased and retractable within the plug body.

Door Inierlocks The alignment linger referred to above can also serve as a key which cooperates with the door for two purposes; the door must be closed before the key is inser-ted and the door must be closed before the plug can be removed from the duct. These actions are very desirable in that a substantially dead-front yaspect is obtained by the door alone, regardless of the insulated or non-insulated nature of the bus bars around the plug-in areas and exposure of the bus bars is kept to an absolute minimum during installation of plugs.

FIGURES 15A-15C illustrate one simple method Afor a door interlock design in which an L-shaped linger 161 is rigidly attached to the line end of the plug body 161a. Finger 161 is preferably made longer than the length of the contact lingers 162 so that these fingers will not interfere with the door while the key linger 161 performs its function. A slot or opening A163 is placed in the duct enclosure 163a adjacent to the door 164 and the plug-in opening 165. Door 164 preferably includes an inwardly bent portion 166 which engages each edge 167 land 168 of plug-in opening 165, thus providing limited motion of door 164 in its open and closed positions. Opening 163 in the duct enclosure 163:1 is not blocked when the door 164 is closed, hence, the L-shaped key linger 161 can enter this opening 163. Opening 163, however, is partially blocked when door -164 is open, and key finger 161 cannot enter opening 163 under this condition. Thus, door 164 must be closed as a first sequence in inserting the plug 161a. Once key finger 161 has entered opening 163, door 164 can be moved into a full open position, after which plug 16111 can be pushed into its full inserted or closed position. In removing plug 161a, its outward motion is restricted by engagement of the upright portion 169 of key linger 161 against door 164. Thus, door 164 must then be closed if plug 161a is to be totally removed from the duct 16311.

While the interlock method described above is very simple, it is often desirable to improve its action to take into account two possible deficiencies. During the insertion of key member 16'1 into opening 163, it is possible to jam contact lingers 162 against door 164. Also, with the plug 161:1 inserted, it is possible to move door 164 toward its closed position so as to make electrical engagement with contact lingers 162 and to cause a short circuit to ground. While it would lbe possible to insulate the lingers 162 or to employ a second interference linger for engagement with door 164 to prevent the door from being closed and to prevent full insertion of plug 161a with door 164 closed, it is more practical to construct the key linger of a Z-shape for these added functions. Such a construction is shown in FIGURES 16A-16G.

A Z-shaped interlock finger 170 is rigidly attached to the line end of a plug body. Finger 170 is made to cooperate with slots in door 171 and plug-in opening 172 in contrast to the previous method where the L-shaped finger was made to cooperate with an opening in the enclosure only. Slot 179 in door 171 is also of a general Z-shape, for cooperation with nger 170, and covers plug-in opening 172. This plugain opening 172 includes a lower notch 172a for purposes later explained. When door 171 is closed and in position over plug-in opening, a slot 173 exists for acceptance of the forward end 174 of the interlock finger 170. Edge 175 abuts against portion 176 of door 171 to prevent further entrance of finger 170 and effectively serves to prevent jamming of contact fingers 177 against door 171. This partial insertion of interlock finger 170 constitutes the first in a sequence of operations.

The second sequence in the operation is to slide door 171 to its open position. During this action, the narrow portion 178 of interlock finger `170 rides in the narrow portion 179 of the Z-shaped slot in door 171. Hence, while door 171 is in a position other than fully closed or fully open, the plug is locked against either further insertion, or removal. When door 171 is fully open, the third operation is to push the plug into its closed or inserted position. This is now possible since key 170 can now enter into portion 180 of the Z-slot of cover 171. Notch 17211 of the plug-in opening 172 is of the same shape as the Z portion 180 and permits the Z- shaped interlock finger 170 to slide past into the duct enclosure 170a.

Once the plug has been started in its travel toward its fully inserted position, door 171 cannot be closed. This is prevented by cooperative engagement between edge 181 of door slot 179, and side 182 of the interlock finger 170. Thus, danger of premature closing of door 171 before the contact fingers have been retracted is eliminated. Engagement of the opposite edge 183 of the door slot 179 against the opposite side 182 of interlock finger 170` also provides an automatic stop of door 171 against motion beyond its full open position. A stop for door 171 in its closed position can Ibe incorporated similar to that shown in FIGURE A in which a bent portion 166 engages edge 168 ofthe plug-in opening.

Retraction of the plug is accomplished in a similar manner to the insertion sequence. When this occurs, tip 184 of interlock key 170 engages portion 185 of door 171 while the door is in the open position. This action prevents complete removal of the plug unless door 171 is first closed, at which time the tip 174 of the interlock finger 170 can be slid past opening 173 of Ydoor 171.

The Z-type of interlock finger basically adds an additional stop for cooperation with the door to overcome the two deficiencies enumerated previously with respect to the L-type finger as described in connection with figures 15A-15C. However, both of these methods employ a rigid finger attached to the line side of the plug body which Imust enter the duct enclosure when the plug is pushed into its inserted or final mounting position. There are some duct `designs which cannot tolerate the full insertion of a long metallic finger by reason of close spacings, uninsulated bars, a narrow duct, etc. In such cases, the interlock finger is stopped from full insertion by the duct enclosure by a bracket 163g (FIGURE 15A). After the door is opened, the plug is inserted into the duct and the finger, being spring loaded, retracts into the plug. A similar arrangement with the Z finger of FIGURE 16A can also include a spring ybiasing means, in which edge 175 of the finger abuts against a filled-in portion of the door previously indicated as 180. In both of these schemes, however, it is still possible to close the door prematurely against the fingers. This restriction in safe operation is eliminated by employing a releasable pin 186 in a slot 187 in the interlock finger 187a as shown in FIGURES 17A-17C. With finger 187a extended, pin 186, spring-biased and part of the plug enclosure, is confined in an upturned portion 187b of the slot 187. This locks the nger 187a. After the sequence of operations as described with respect to FIGURE 16A is performed, -pin 186 is pushed downward and interlock finger 187a can be retracted along the side of the plug against spring 188. Entrance of interlock finger 187a into the duct is prevented :by abutment of edge 189 of the finger against side 190 of the door. As another construction, it is possible to incorporate a rigid interlock finger as part of the flange enclosure or the end plate of the two piece plug device shown in FIGURES 4A and 5A respectively. In these cases, the finger is stationary and does not move when the plug body is pushed against the duct. Its function then becomes one similar to the L-shaped finger described with respect to FIGURES 15A where it acts in conjunction with the duct enclosure, or it can be similar to the Iforward portion of the Z-shaped finger of FIGURE 16A acting in conjunction ywith slots 173 and 179' of the door.

There are instances where it would be desirable to have the interlock finger retractable and locked in the plug. Such cases exist where the interlock to the door may want to be voidable as for inspection, or where the same plug having an interlock finger would be placed on a different duct design having no interlock type of door. In these events, the nger can be arranged to be either partially or completely retractable within the plug with a screw for locking purposes. Alternatively and in combination, the door can be arranged with a screw acting as a stop member in pla-ce of the rbent over tab, such as shown at 166 in FIGURE 15A. The screw is removable so that the door can slide past its normal open position, thus allowing freedom for the interlock finger to move unrestricted into and out of Athe duct without interference by the door. In this instance, that portion of the door defined `by edge 183 in FIGURE 16B can be slotted so that there will be no interference with the side opposite 182 of the key. Naturally, the screw can be made to abut the open edge of the plug-in opening to serve `as a normal door open position stop.

All of the above methods for engagement of a finger from the plug with slo-ts in a plug-in door for interlock purposes are, of course, adaptable to any type of plug, irrespective of any temporary holding means. It is obvious, however, that a means for temporary support of the plug will make operation of the interlock simpler and more practical since the installer is free of the weight of the plug.

Switch Interior/cs Switch interlocks between plugs and the duct enclosure are necessary from a safety standpoint since they prevent contact finger engagement or disengagement from the bus bars while the switching contacts within the plug are in an On position. FIGURES 18A-18C illustrate one method for accomplishing such a function. The plug body 19261 of FIGURE 18A incorporates a molded case circuit breaker 193 as one form of switching device. A U-shaped bracket 194 is pivotally attached to the sides of the plug enclosure 192e at 195 and extends around the top of the circuit breaker 193 so as to be operatively connected 'to the breaker handle 196. Hence, operating the breaker handle 196 will also swing the bracket 194 about its pivot points 195. An interlock lever 197 is pivotally attached to one side of the plug enclosure at 198. Connecting the interlock lever 197 and the U-shaped bracket 194 is another member 199 whose function is t0 rotate the interlock lever 197 when handle 196 of the circuit breaker 193 is moved. A slot 200 exists in duct casing 192g which is just wide enough to receive the forward end 201 of the interlock lever 197. When the plug device is turned to an On position, the interlock finger 197 is rotated so that a notch portion 202 engages end portion 203 of the slot in the duct enclosure 192g. 

